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DETERMINATION OF MOLECULR

one  atom   of hydrogen.     Consequently^ the  observed density
must be  multiplied  by two in ordeX^p" o]^s^-

weight compared with one atom of hydrog^L, "; •' V Q £[^ Q p- '**~ '.

Vapour Density Method (Victor" Meyer). —This
method, which is generally employed for substances which
volatilise without decom-
position, is known as the
air displacement method
of Victor Meyer. It con-
sists in rapidly vaporising
a known weight of a sub-
stance at a constant tem-
perature at least 40 — 50°
above its boiling-point in
a special form of appar-
atus, which admits of the
displaced air being col-
lected and measured. The
volume occupied by a
given weight of the sub-
stance under known con-
ditions is thus ascertained
and from these data the
density is calculated. The
following apparatus is re-
quired : —

I. A Victor Meyer Ap-
paratus as shown in
Fig. 27. It consists of
an elongated glass bulb
with a narrow stem, and
a capillary side-tube. It
is provided with a well-
fitting rubber cork, which

can be pressed easily and                        FIG. 27.

tightly into the open end

of the stem. The apparatus is clamped within an outer
jacket of tin plate or copper, which holds the boiling liquid
'required to produce a constant temperature. It is representeej^
as transparent in the Fig.                 y* \ ' \ _ . ••

"*':

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